Blind loop syndrome occurs when part of the small intestine forms a loop that food bypasses during digestion. The presence of this "blind loop" means food may not move normally through the digestive tract.

Slowly moving food and waste products become a breeding ground for bacteria. The result — bacterial overgrowth — often causes diarrhea and may cause weight loss and malnutrition.

Sometimes called stasis syndrome or stagnant loop syndrome, blind loop syndrome is often a complication of stomach (abdominal) surgery. But blind loop syndrome can also result from structural problems and some diseases. Sometimes surgery is needed to correct the problem, but antibiotics are the most common treatment.

Signs and symptoms of blind loop syndrome often include:

Loss of appetite

Abdominal pain

Nausea

Bloating

An uncomfortable feeling of fullness after eating

Diarrhea

Unintentional weight loss

When to see a doctor

Bloating, nausea and diarrhea are signs and symptoms of many intestinal problems. See your doctor for a full evaluation — especially if you've had abdominal surgery — if you have:

Persistent diarrhea

Rapid, unintentional weight loss

Abdominal pain lasting more than a few days

If you have severe abdominal pain, get immediate medical care.

The small intestine is the longest section of your digestive tract, measuring about 20 feet (6.1 meters). The small intestine is where food mixes with digestive juices and nutrients are absorbed into your bloodstream.

Unlike your large intestine (colon), your small intestine normally has relatively few bacteria. But in blind loop syndrome, stagnant food in the bypassed small intestine becomes an ideal breeding ground for bacteria. The bacteria may produce toxins as well as block the absorption of nutrients.

The greater the length of small bowel involved in the blind loop, the greater the chance of bacterial overgrowth.

What triggers blind loop syndrome?

Blind loop syndrome can be caused by:

Complications of abdominal surgery, including gastric bypass for obesity and gastrectomy to treat peptic ulcers and stomach cancer

Structural problems in and around your small intestine, including scar tissue (intestinal adhesions) on the outside of the bowel and small, bulging pouches of tissue that protrude through the intestinal wall (diverticulosis)

Damage to the intestinal lining. Toxins that are released when bacteria break down stagnant food harm the mucous lining (mucosa) of the small intestine. As a result, most nutrients, including carbohydrates and proteins, are poorly absorbed, leading to serious malnourishment.

Vitamin B-12 deficiency. Bacteria in the small intestine absorb vitamin B-12, which is essential for the normal functioning of your nervous system and the production of blood cells and DNA. A severe B-12 deficiency can lead to weakness, fatigue, tingling and numbness in your hands and feet, and, in advanced cases, to mental confusion. Damage to your central nervous system resulting from a B-12 deficiency may be irreversible.

Brittle bones (osteoporosis). Over time, damage to your intestine from abnormal bacterial growth causes poor calcium absorption, and eventually may lead to bone diseases, such as osteoporosis.

Kidney stones. Poor calcium absorption may also eventually result in kidney stones.

If you have signs and symptoms that are common to blind loop syndrome, make an appointment with your doctor. After an initial evaluation, you may be referred to a doctor who specializes in treatment of digestive disorders (gastroenterologist).

Here's some information to help you get ready for your appointment, and what to expect from your doctor.

Information to gather in advance

Write down your symptoms, including when they started and how they may have changed or worsened over time.

Bring your medical records, especially if you have had surgery on your stomach or intestines, have any known bowel condition, or have received radiation to the abdomen or pelvis.

Make a list of all your medications, vitamins and supplements.

Write down your key medical information, including other conditions with which you've been diagnosed. Be sure to let your doctor know about any abdominal surgery you've had.

Write down key personal information, including any recent changes or stressors in your life. These factors can be connected to digestive signs and symptoms.

Take a family member or friend along, if possible. It can be difficult to remember all the information provided during an appointment. Someone who accompanies you may remember something that you missed or forgot.

Write down questions to ask your doctor. Creating your list of questions in advance can help you make the most of your time with your doctor.

Are there any side effects associated with the medications you're prescribing?

I have other conditions. How can I treat them?

Will I need to stay on medications long term?

How often will you see me to monitor my progress?

Should I take any nutritional supplements?

Do I have any vitamin deficiencies?

Are there any lifestyle or dietary changes I can make to help reduce or manage my symptoms?

What to expect from your doctor

Your doctor is likely to ask you a number of questions. Being ready to answer them may reserve time to go over points you want to spend more time on. You may be asked:

Have you ever had abdominal surgery?

What are your symptoms?

When did you first notice these symptoms?

Do your symptoms come and go or stay about the same?

Is your pain cramp-like?

Does your pain radiate to other parts of your abdomen or to your back?

Have you lost weight without trying?

Have you noticed a change in your stools?

Have your signs and symptoms included vomiting?

Have your signs and symptoms included a fever?

Has anyone close to you had similar signs or symptoms recently?

What is your typical daily diet?

Have you ever been diagnosed with a food allergy or with lactose intolerance?

Have you been diagnosed with any other medical conditions?

What medications are you taking, including prescription and over-the-counter medications, vitamins, herbs and supplements?

Do you have any family history of bowel disorders or colon cancer?

Have you ever had radiation therapy to your abdomen or pelvis?

Have you ever had kidney stones?

Have you ever had problems with your pancreas?

Do you have Crohn's disease?

The first step in diagnosing blind loop syndrome is usually an imaging test, such as:

Abdominal X-ray

Abdominal CT scan

You may have additional tests to check for bacterial overgrowth in your small intestine, poor fat absorption, or other problems that may be causing or contributing to your symptoms:

Barium X-ray of the small intestine. This test uses a contrast solution (barium) to coat the lining of your intestine so that it stands out clearly on X-rays. A barium X-ray may reveal a blind loop, diverticulosis, a narrowing (stricture) of the intestine or other structural problems, as well as slow transit times that can cause bacterial overgrowth.

CT enterography. This test is more sensitive than is a barium X-ray or conventional CT. It helps detect inflammation or structural problems in the bowel and abnormalities in other organs, such as the pancreas.

Hydrogen breath test. This test measures the amount of hydrogen that you breathe out after drinking a mixture of glucose and water. A rapid rise in hydrogen indicates poor carbohydrate digestion and bacterial overgrowth in your small intestine. Although widely available, this test is less sensitive than other breath tests.

D-xylose breath test. This test, which is more accurate than a hydrogen breath test, measures the amount of carbon dioxide in your breath. High levels of carbon dioxide suggest bacterial overgrowth.

Bile acid breath test. Bile acids from your liver help digest fats (lipids) in your small intestine. Bacterial overgrowth interferes with the process. This test uses a bile salt with a radioactive tracer to check for bile salt dysfunction.

Quantitative fecal fat test. This test can determine how well your small intestine absorbs fat. You eat a high-fat diet for three days, and the amount of fat in your stool is then measured. Large amounts of undigested fat may be caused by bacterial overgrowth, but more commonly result from other conditions such as short bowel syndrome or chronic pancreatitis.

Small intestine aspirate and fluid culture. This is the most sensitive test for bacterial overgrowth. To obtain the fluid sample, doctors pass a long, flexible tube (endoscope) down your throat and through your upper digestive tract to your small intestine. A sample of intestinal fluid is withdrawn and then tested in a laboratory for the growth of bacteria.

If your doctor believes that bacterial overgrowth is very likely, he or she may begin treatment with antibiotics immediately without specific testing.

Antibiotic therapy

For most people, the initial way to treat bacterial overgrowth is with antibiotics. Doctors may start this treatment if your symptoms and medical history strongly suggest this is the cause, even when test results are inconclusive or without any testing at all. Testing may be performed if antibiotic treatment is not effective.

A short course of antibiotics often significantly reduces the number of abnormal bacteria. But bacteria can return when the antibiotic is discontinued, so treatment may need to be long term. Some people with a blind loop may go for long periods without needing antibiotics, while others may need them regularly.

Doctors may also switch among different antibiotics to help prevent bacterial resistance. Antibiotics wipe out most intestinal bacteria, both normal and abnormal. As a result, antibiotics can cause some of the very problems they're trying to cure, including diarrhea. Switching among different drugs can help avoid this problem.

Nutritional support

Correcting nutritional deficiencies is a crucial part of treating blind loop syndrome, particularly in people with severe weight loss. Malnutrition can be treated, but the damage it causes can't always be reversed.

These treatments may improve vitamin deficiencies, reduce intestinal distress and help with weight gain:

Nutritional supplements. People with blind loop syndrome may need intramuscular injections of vitamin B-12, as well as oral vitamins, calcium and iron supplements.

Lactose-free diet. Damage to the small intestine may cause you to lose the ability to digest milk sugar (lactose). In that case, it's important to avoid most lactose-containing products, or use lactase preparations that help digest milk sugar.

Some people may tolerate yogurt because the bacteria used in the culturing process naturally break down lactose.

Medium-chain triglycerides. Most dietary fats consist of a long chain of fat molecules (triglycerides). Some people with blind loop syndrome have an easier time digesting medium-chain triglycerides, found in coconut oil.

Medium-chain triglycerides are sometimes prescribed as a dietary supplement for people with severe blind loop syndrome resulting in short bowel syndrome.

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